This invention relates to a motive power generating device in which electromagnets and a combination of a magnetic material and a permanent magnet are used as a stator and a rotator, respectively. More particularly, the invention relates to a motive power generating device which transforms magnetic energy into operative energy with maximum efficiency utilizing a magnetic force inherent in a permanent magnet as an energy source.
Heretofore, it has been known in the art that a motive power generating device in which electromagnets and a combination of a magnetic material, such as soft steel, and a permanent magnet are used as a stator and a rotator, respectively. Such a device includes, for example, a step motor of a HB (Hybrid) type.
FIGS. 12 to 17 diagrammatically illustrate an example of conventional HB type step motors. The HB type motor is characterized by a rotor 52, as shown in FIGS. 12 and 13. The rotor combines the advantageous feature of a step motor of a VR (Variable Reluctance) type in that a smaller step angle may be obtained by virtue of the teeth formed in a laminated steel plate 53 constituting one component of the rotor, with the advantageous feature of a step motor of a PM (Permanent Magnet) type in that a high degree of efficiency and miniaturization may be obtained by virtue of the permanent magnet 54 constituting the other component of the rotor 52. It is to be noted here that the steel core of the stator 50 is the same as that of a VR type motor, but the method of winding and connecting the coils is different.
FIG. 14 shows a passage of magnetic flux (magnetic path) created by the permanent magnet 54. The magnetic path represents a distribution of a uni-polar type in which an N-pole or S-pole uniformly appears at the axial ends of a rotor shaft 55. On the other hand, FIG. 15 shows a magnetic path created by the electromagnets 51 of the rotor 50. The magnetic path represents a distribution of a hereto-polar type in which an even number of magnetic poles in the order, for example, of NSNS . . . appear in a plate vertical to the rotor shaft 55. The uni-polar magnetic flux of the permanent magnet (magnetic field of the permanent magnet) and the hereto-polar magnetic flux of the windings (magnetic field of the electromagnet) interact with each other so as to generate a torque. The term "interaction between the magnetic flux of the permanent magnet and the magnetic flux of the windings" is used herein to mean that an inclination of the line of magnetic force is created in the gap between the permanent magnet 54 and the electromagnet 51.
A torque generating mechanism of the HB type motor will be explained with reference to FIGS. 16 and 17 illustrating a model developed into a form of a linear motor. FIG. 16 shows a cross-section of S-side (south pole side) of the permanent magnet 54, while FIG. 17 shows a cross-section of N-side (north pole side) of the permanent magnet. In these drawings, magnetic flux emanating from the electromagnets 51 is shown by solid lines, and magnetic flux emanating from the permanent magnet 54 is shown by dotted lines.
With regard to the magnetic field from the electromagnets 51 (refer to the solid line in FIGS. 16), the S-side cross-section of the permanent magnet 54 shows that the line of magnetic force in the central gap is inclined in the downward and right hand direction, while the line of magnetic force in the right hand end gap is inclined in the upward and right-hand direction. Thus, the lines of magnetic force in the above two gaps tend to cancel each other out. The same relationship is applied to the cross section of the N-side (north pole side) of the permanent magnet 54.
It is noted that torque will be generated when the magnetic field of the electromagnet 51 and the magnetic field of the permanent magnet 54 interact with each other. Specifically, and with regard to the central gap in the S-side cross-section of the permanent magnet 54, i.e., N-side of the electromagnet 51, the magnetic field of the electromagnet 51 and the magnetic field of the permanent magnet 54 interact with each other strongly in the same direction so as to generate in the rotor 52 a propulsive force toward the left in FIG. 16. On the other hand, and with regard to the right-hand gap, i.e., S-side of the electromagnet 51, both magnetic fields interact with each other weakly in opposite directions, so as to generate a propulsive force toward the right in FIG. 16. It is noted, however, that the propulsive force generated toward the right in FIG. 16 is relatively small. Consequently, a stronger propulsive force toward the left in FIG. 16 is generated.
With regard to the central gap in N-side cross-section of the permanent magnet 54, i.e., N-side of the electromagnet 51, the magnetic field of the electromagnet 51 and the magnetic field of the permanent magnet 54 interact with each other weakly in opposite directions, so as to generate in the rotor 52 a propulsive force toward the right in FIG. 17. The resultant propulsive force is relatively small. On the other hand, and with regard to the right-hand gap in FIG. 17, i.e., S-side of the electromagnet 51, both magnetic field interact strongly with each other in the same direction, so as to generate a propulsive force of relatively significant magnitude toward the left in FIG. 17. Consequently, a stronger propulsive force toward the left in FIG. 17 will be generated. Accordingly, the thus generated propulsive force causes the rotor to be advanced in the left-hand direction in FIGS. 16 and 17.
It should be noted, however, that such a conventional HB type motor involves a problem in that a force acting in an opposite direction to the torque (a force tending to interfere with rotation of the rotor 52) is generated as mentioned above. In view of electrical energy to be applied to the windings of the electromagnets 51, an electric current applied to the winding of the right-hand end electromagnet in FIG. 16 and the winding of the central electromagnet in FIG. 17 is merely consumed so as to cancel the magnetic field of the permanent magnet which tends to prevent rotation of the rotor 52. Thus, such an electric current does not effectively contribute at all to the movement of the rotor 54, thus decreasing energy efficiency. In view of the magnetic energy of the permanent magnet 54, such energy is utilized together with the magnetic field created by the electromagnet 51, but it partly interferes with the movement of the rotor 52. Thus, magnetic energy of the permanent magnet 54 is not effectively utilized.
The above problem experienced with the HB type motor applies equally to motive power generation devices in which an electromagnet is used as a stator and soft steel and a permanent magnet is used as a rotor.